From 13594b7146cc4791625280123a6071805a0be7c3 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Mon, 28 Dec 2020 23:51:24 +0100
Subject: [PATCH] LibGfx+AK: Make text elision work with multi-byte characters

This was causing WindowServer and Taskbar to crash sometimes when the
stars aligned and we tried cutting off a string ending with "..." right
on top of an emoji. :^)
---
 AK/Utf32View.h               | 7 +++++++
 AK/Utf8View.cpp              | 2 +-
 AK/Utf8View.h                | 7 ++++++-
 Libraries/LibGfx/Painter.cpp | 5 +++--
 4 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/AK/Utf32View.h b/AK/Utf32View.h
index 49b8efb13cc..95c8d29e123 100644
--- a/AK/Utf32View.h
+++ b/AK/Utf32View.h
@@ -105,6 +105,13 @@ public:
     bool is_empty() const { return m_length == 0; }
     size_t length() const { return m_length; }
 
+    size_t iterator_offset(const Utf32CodepointIterator& it) const
+    {
+        ASSERT(it.m_ptr >= m_code_points);
+        ASSERT(it.m_ptr < m_code_points + m_length);
+        return ((ptrdiff_t)it.m_ptr - (ptrdiff_t)m_code_points) / sizeof(u32);
+    }
+
     Utf32View substring_view(size_t offset, size_t length) const
     {
         if (length == 0)
diff --git a/AK/Utf8View.cpp b/AK/Utf8View.cpp
index 63ae61658d8..f43ee1b0cd4 100644
--- a/AK/Utf8View.cpp
+++ b/AK/Utf8View.cpp
@@ -65,7 +65,7 @@ Utf8CodepointIterator Utf8View::end() const
     return { end_ptr(), 0 };
 }
 
-int Utf8View::byte_offset_of(const Utf8CodepointIterator& it) const
+size_t Utf8View::byte_offset_of(const Utf8CodepointIterator& it) const
 {
     ASSERT(it.m_ptr >= begin_ptr());
     ASSERT(it.m_ptr <= end_ptr());
diff --git a/AK/Utf8View.h b/AK/Utf8View.h
index 5270addd4a9..bfb5d489b32 100644
--- a/AK/Utf8View.h
+++ b/AK/Utf8View.h
@@ -76,10 +76,15 @@ public:
 
     const unsigned char* bytes() const { return begin_ptr(); }
     int byte_length() const { return m_string.length(); }
-    int byte_offset_of(const Utf8CodepointIterator&) const;
+    size_t byte_offset_of(const Utf8CodepointIterator&) const;
     Utf8View substring_view(int byte_offset, int byte_length) const;
     bool is_empty() const { return m_string.is_empty(); }
 
+    size_t iterator_offset(const Utf8CodepointIterator& it) const
+    {
+        return byte_offset_of(it);
+    }
+
     bool validate(size_t& valid_bytes) const;
     bool validate() const
     {
diff --git a/Libraries/LibGfx/Painter.cpp b/Libraries/LibGfx/Painter.cpp
index ca96ef068ba..70aa7ec77f1 100644
--- a/Libraries/LibGfx/Painter.cpp
+++ b/Libraries/LibGfx/Painter.cpp
@@ -918,7 +918,8 @@ void draw_text_line(const IntRect& a_rect, const TextType& text, const Font& fon
             int new_width = font.width("...");
             if (new_width < text_width) {
                 size_t offset = 0;
-                for (auto code_point : text) {
+                for (auto it = text.begin(); it != text.end(); ++it) {
+                    auto code_point = *it;
                     int glyph_width = font.glyph_or_emoji_width(code_point);
                     // NOTE: Glyph spacing should not be added after the last glyph on the line,
                     //       but since we are here because the last glyph does not actually fit on the line,
@@ -927,7 +928,7 @@ void draw_text_line(const IntRect& a_rect, const TextType& text, const Font& fon
                     if (width_with_this_glyph_included > rect.width())
                         break;
                     new_width += glyph_width + glyph_spacing;
-                    offset++;
+                    offset = text.iterator_offset(it);
                 }
                 apply_elision(final_text, elided_text, offset);
             }